In this study, the effects of 10 mm bilaterally applied basalt and glass fiber reinforced (BRC and GRC) cementitious plasters with different fiber content (1.0%, 2.0% and 3.0%) on the behavior of the autoclaved aerated concrete (AAC) block infill walls were investigated. For this purpose, 8 infill walls with dimensions of 150 × 150 × 20 cm were produced to examine the behavior of the infill walls under reversed cyclic loading. The load carrying capacities, stiffness degradation and energy dissipation capacities of the infill walls placed in a steel frame with hinges on all four corners were determined by using hysteretic load–displacement curves to evaluate effects of fiber reinforced cementitious plaster. The test results show that BRC and GRC plaster applications considerably increase the load carrying and energy dissipation capacities of the infill walls. However, the experimental results illustrated that the usage of BRC plasters in strengthening of the AAC block infill walls needs more attention. Having similar results for different fiber ratios in the use of GRC reveals that it may be more rational to use 1.0% fiber content for the most economical solution for strengthening. Although the results obtained in this study are valid for infill walls, the experimental results show that GRC plasters can also be used in strengthening of masonry walls. It is recommended that this method can be used quickly and effectively in strengthening of masonry structures, which occupy an important place in the existing building stock.